DISPERSION COMPENSATION IN OPTICAL COMMUNICATION SYSTEM BY EMPLOYING 16-QAM MODULATION USING OFDM

Next generation communication network will be required to provide increased data rate efficiently along with the flexibility to adapt to various dynamic traffic patterns in a cost effective manner. The optical fiber communication system can do the same along with low losses and good quality of transmission. In the recent past, the enormous growth of network traffic on deployed optical communication networks forced the demand for a more constructive utilization of the channel capacity of the optical fiber communication channel. In near future, the next generation optical links are going to carry 10 / 40 Gbps per wavelength. The two windows at 1310 & 1550 nm provide low attenuation with transmission bandwidth of approximately 50 Tbps. Optical fiber communication system are primarily operated at wavelength near 1550 nm in order to match with the minimum loss point of silica fiber and hence maximize transmission distance. Unluckily, at this wavelength dispersion restricts the achievable transmission distance. As the data transmission rate increases the dispersion causing pulse broadening results in Inter-Symbol Interference (ISI). The dispersion restricts the highest transmission data rate and longest transmission distances for the repeater less optical communication link [1]. Various endeavors have been inscribed for the advancement of dispersion compensating techniques and devises to recuperate the pulse broadening due to ISI. The OFDM is a highly spectral efficient, multiple sub-carrier modulation technique. It have dynamic tolerance to dispersion, thereby making it an excellent dispersion compensation scheme for using the exiting optical communication networks for next generation dynamic traffic pattern. It overcomes the problem of ISI due to dispersion, by simultaneously modulating and transmitting a number of orthogonal sub-carriers at a low symbol rate, which makes the symbols period much longer than the channel impulse response. This work investigates the use of OFDM as a technique to fulfil these needs for next generation optical communication system. These involve design, modelling, simulation and comparative performance analysis of the optical communication system with and without using OFDM for dispersion compensation. A novel scheme of tuneable dispersion compensation using OFDM is presented in this work. The system performance has been analyzed in terms of BER, constellation diagrams and OSNR. OFDM is shown to outperform in high data rate optical communications system for the long haul high data rate transmission with high bandwidth utilization efficiency. Therefore, the combination of optical system and OFDM is the highly efficient technique for the next generation long haul high capacity communication network